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Tuesday, December 14, 2010

Andrew Glikson: Antarctic blues and the Australian drought

This is a repeat -- but it is such a nice one!

Antarctic blues and the Australian drought

Andrew Glikson
Earth and paleo-climate scientist
Australian National University

The Antarctic ice sheet has not always been there.

The ice began to form about 34 million years ago, by the late Eocene, when the Antarctic continent (Fig. 1) became isolated through the opening of the Drake Passage between the Antarctic peninsula and southern tip of South America, restricting access of warm currents, and when global carbon dioxide levels decreased to below 450 parts per million CO2, decreasing the mean temperature of Earth by near -6 °C [1].

Fig. 1. The Antarctic continent from space

The current global rise in atmospheric CO2 levels to 387 ppm (over 400 ppm-e radiative equivalent of CO2 + CH4 + N2O) ensues in warming of the Antarctic ice, in particular of western Antarctica, and of the Antarctic peninsula (Fig. 2). It further reduces concentration of circum-Antarctic sea ice (Fig. 3). Another expression of warming is the accelerating movement of glaciers, where the mass of the ice sheet decreased significantly at a rate of 152 ± 80 cubic kilometers of ice per year [2].

Based on a combination of ground stations and satellite observations, NASA/GISS reports a mean temperature increase of +0.12 °C per decade for the entire continent of Antarctica, and +0.17 °C per decade for western Antarctica, during 1957-2006 (NASA, 21.1.2009) (Fig. 2). Manifestations of warming include reduced concentration of sea ice around parts of Antarctica (Fig. 3) and the disintegration of ice shelves (Fig. 4) due to the effect of warming seas. In particular, the part of western Antarctica which overlies sub-sea level basement is vulnerable to sea water-induced melting. While most of the peripheral near-coastal zones of west and east Antarctica display various degrees of warming and glacier melt, a small area in east Antarctica have been cooling, a likely result of ozone depletion above Antarctica, ozone being a greenhouse gas, as well as acceleration and wind-chill effect of the Antarctic wind vortex (Fig. 5).

Fig. 2. NASA Goddard Institute of Space Science, 21.1.2009. Satellite and ground station data confirm 50 years of west Antarctica warming. Values in °C over 50 years.

Fig. 3. Sea ice per cent concentration trends in the Arctic Sea and around Antarctica for October 2008 relative to 1979-2000 October monthly average. National Snow and Ice Data Center.

Regional changes in atmospheric circulation and associated changes in sea surface temperature and sea ice are required to explain the enhanced warming inWestern Antarctica [3]. Breakup of ice shelves is exemplified by the Wilkins ice shelf (Fig. 4), which for the first time continued to breakdown during winter (June-July) 2008 [4].

Fig. 4. Satellite images shows the Wilkins Ice Shelf as it began to break up. The large image is from March 6; the images at right, from top to bottom, are from February 28, February 29, and March 8. NSIDC processed these images from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, which flies on NASA’s Earth Observing System Aqua and Terra satellites.

The southward migration of climate zones by nearly 400 km and the retreat of the Antarctic wind vortex (Fig. 5) have combined to increase drought conditions in southern Australia. In the last thirty years, a 20% loss of the average rainfall along Australia's southern fringe occurred, marked by sudden drops in rainfall in southwestern Australia in the 1970s, and in Victoria in the 1990s, affecting agriculture and reservoir supplies for more than six million people [5]. The consequences in terms of maximum temperature rise (Fig. 6A), rainfall variations (Fig. 6B), and extreme heat wave conditions (Fig. 6C) are evident.

Figure 5. The Antarctic wind vortex viewed from the Galileo spacecraft. As climate zones migrate toward the poles, the southward contraction of the swirling cold moist fronts results in reduced rainfall over southern Australia.

Loss of Antarctic ice shelves and ice sheets, indicated by time variable gravity show mass loss [2] threatens to raise sea levels on the scale of many metres, leading to inundation of coastal regions, deltas, and low river valleys around the world (Fig. 7). Melting of western Antarctic ice would raise sea levels by nearly 7 metres, whereas melting of the entire Antarctic ice sheet would raise sea levels by some 70 metres, returning the Earth to pre-late Eocene conditions (Fig. 6).

Figure 6A. Australia maximum temperature variations in °C per 10 years, 1970-2008 (Australian Bureau of Meteorology).

Figure 6B. Australia annual total rainfall variations in mm per 10 years, 1970-2008 (Australian Bureau of Meteorology).

Figure 6C. Maximum temperatures for Australia, 7 February 2009. Australian Bureau of Meteorology.

Fig. 7. Projected sea level rise (Hansen, 2007). The color bars represent topographic elevations in metres. Sea level rise by up to 25 metres (Greenlandand western Antarctic ice melt) is represented in blues, and up to 75 metres (total Antarctic melt) in yellow.

Until recently, whenever climate research organizations reported increases in Arctic Sea ice melt rates [6], advocates of global “cooling” have been making references to the Antarctic continent as a supposed counter argument [7]. Referring to small, stable or slightly cooling parts of east Anarctica (Fig 2), a plethora of bogus climate websites claims Antarctic warming is not a part of global warming [8].

Presumably regarding Antarctica as part of another planet?

Nor do “climate skeptics” shed too many tears about Emperor penguins, the magnificent birds which have to migrate from their inland colonies across ice shelves and sea ice (Fig. 8), where the females lay just one egg that is tended by the male. The ice plays a major role in their overall breeding success. Further, the extent of sea ice cover influences the abundance of krill and the fish species that eat them – both food sources for the penguins.

Misreadings of climate science by “climate skeptics” have delayed efforts at climate mitigation by at least 20 years. In the words of Clive Hamilton [9]: “If scientific advances cause scientists to reject the conclusions of past IPCC reports … not much harm will be done. … but if … fellow skeptics were successful in stopping policies to cut emissions and the IPCC projections turn out to be correct, then environmental catastrophe will follow and millions of people will die. Do they lose sleep over this? Do they worry about how their grandchildren will see them? Or are they so consumed by the crusade that they know they will never be proven wrong?”

Fig. 8. Melting Antarctic iceberg.


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